Project Summary The proposed work on infant walking tests critical hypotheses about the development of behavioral flexibility, a fundamental hallmark of motor skill. Flexibility is the ability to tailor motor actions to changes in body-environment relations. Flexibility is essential to functional, adaptive action because the body and environment are always in flux. Changes in local conditions?body growth, variations in clothing/footgear, carrying objects, variations in ground surfaces, elevations, and obstacles in the path? alter the biomechanical constraints on action. One theory of flexibility claims that learning particular solutions to particular motor problems cannot ensure the ability to cope with the novelty and variability that characterize everyday activity. Rather, infants must learn HOW to solve new motor problems by exploring the current body-environment relations, discerning the critical information regarding which actions are possible, and assembling appropriate solutions in the moment. The proposed experiments will test critical hypotheses generated by this theory. Aim 1 tests the hypothesis that flexibility in infant walking generalizes across tasks with different body-environment relations. We will test individual infants (from novice to experienced walkers) in four tasks?at the edge of a precipice on slopes, drop-offs, bridges, and gaps. We predict that flexibility will generalize across tasks and the level of flexibility across tasks depends on the duration of infants' everyday walking experience. We also predict that more efficient, discerning exploratory behaviors predict higher levels of flexibility. Aim 2 tests the hypothesis that experience with varied body-environment relations promotes flexibility. Merely repeating the same actions over and over should not lead to flexibility. We will compare responses by infants receiving intense training on a ?body-environment obstacle course? to infants receiving sham training and infants receiving only everyday walking experience. Aim 3 will identify critical factors that instigate infants' experience with varied body-environment relations by comparing infants' spontaneous locomotor activity in four toy conditions and two social-interaction conditions. The proposed studies use innovative procedures (a ?body-environment obstacle course,? a new cross-task normalization method, new ways of using head-mounted eye tracking) and technologies (instrumented playroom floor to record spontaneous walking, gait modifications, standard measures of gait maturity, path shape, distance travelled, and area explored) to move the field forward. The rich, detailed data will be shared in the Databrary library for other researchers and clinicians to use to ask new questions outside the scope of the proposed project. Findings will have important implications for preventing accidental injury from falling from a height, a leading cause of injury in infants. A Scientific Advisory Committee for Translational Clinical Science will ensure the clinical relevance of the work.